Oxychlorination catalyst compositions for the production of chlorinated hydrocarbons by oxychlorination have been well established for many years. Oxychlorination is the reaction of a hydrocarbon, such as ethylene or propylene, with hydrogen chloride and oxygen to form water and the corresponding chlorinated hydrocarbons, such as 1,2-dichloroethane (EDC) or 1,2-dichloropropane, preferably in the presence of an oxychlorination catalyst. The oxychlorination reaction has been applied worldwide in large industrial scale. For example, the conversion of ethylene to EDC by oxychlorination alone is currently in a scale of million's of tons per year.
One particular method of oxychlorination is the vapor phase reaction of a hydrocarbon, such as ethylene or propylene, with a mixture of hydrogen chloride (HCl) and a source of oxygen (such as high purity oxygen obtained from an air separation plant where pressure swing absorption or cryogenic separation is employed to remove inert materials, or a dilute oxygen stream such as air or a mixture of oxygen and at least an inert gas) within a fluidized catalyst bed comprising an oxychlorination catalyst. A typical oxychlorination catalyst can comprise a metal salt such as copper chloride and optionally at least a salt of alkali metals, alkaline metals or rare earth metals deposited on or combined with a support material or inert carrier, such as particles of silica, alumina, kieselguhr, fuller's earth, clays and alumina silicates or aluminum silicates or aluminium silicates. For use in fluid-bed catalysis, the support material should be readily fluidizable having the proper particle density, resistance to attrition, and particle size distribution to be useful in the process without generating excessive catalyst loss from the reaction zone. Optionally, the catalyst composition may comprise a diluent which comprises catalytically and chemically inert particles such as alumina and silica having a low surface area.
In the oxychlorination of a hydrocarbon (e.g., ethylene), it is desirable for the oxychlorination catalyst composition to effect a high yield of the desired chlorinated product (e.g., EDC) and a small amount of by-products such as carbon dioxide, carbon monoxide and other chlorinated materials. In the high volume business of manufacturing EDC, a small increase in the efficiency of ethylene conversion to EDC can provide significant cost savings. Furthermore, an increase in ethylene efficiency or selectivity of ethylene to EDC can reduce the amount of by-products produced, the associated costs to dispose of them properly, and the potential risks to the environment. Selectivity of ethylene to EDC (i.e., ethylene selectivity) is the number of moles of pure EDC produced per 100 moles of ethylene consumed or converted (i.e., ethylene conversion) to EDC plus any by-products, whereas ethylene efficiency is defined as the product of ethylene selectivity times ethylene conversion. Similarly, selectivity of HCl to EDC (i.e., HCl selectivity) is the number of moles of pure EDC produced per 200 moles of HCl consumed or converted (i.e., HCl conversion) to EDC plus any by-products, whereas HCl efficiency is defined as the product of HCl selectivity times HCl conversion. Similarly, selectivity of oxygen to EDC (i.e., oxygen selectivity) is the number of moles of pure EDC produced per 50 moles of oxygen consumed or converted (i.e., oxygen conversion) to EDC plus any by-products, whereas oxygen efficiency is defined as the product of oxygen selectivity times oxygen conversion.
It is also desirable, for economic and environmental reasons, for the oxychlorination catalyst composition to effect a high conversion of HCl used in the reaction. Unconverted HCl needs to be neutralized by a base and the resulting salt must be disposed. Also, high levels of unconverted HCl in the process generally leads to high HCl “break through” downstream in the reactor which can cause corrosion problems. Hence, it is desirable to operate a reactor at an optimal temperature to provide high HCl conversion. In commercial applications, a combination of high HCl conversion and high ethylene efficiency or selectivity of ethylene to EDC is most desirable.
Further, it is desirable to increase the optimal operating temperature of the oxychlorination catalyst without sacrificing catalyst performance because it would be the most cost efficient way to increase the production capacity of an existing oxychlorination reactor. In general, an increase in the operating temperatures increases the temperature difference between the fluidized catalyst bed and the steam drum, which is utilized for removing the heat of reaction and maintaining the controlled temperature. Therefore, increasing the operating temperature can increase the driving force for heat removal and allow for increased reactor productivity. The optimal operating temperature for the catalyst in reactors where the majority of the vent gas is recycled back to the reactor is the point where the HCl conversion and the ethylene selectivity are optimized. For air-based, once-through reactors, the optimal operating temperature is the point where the HCl conversion and the ethylene efficiency are optimized. For example, for a reactor limited by a steam drum pressure of 211 psig (i.e., 1455 kPa) and/or 200° C., an increase in the optimal operating temperature of the oxychlorination catalyst composition from 230° C. to 240° C. would result in an increase of 33% in the production capacity of that reactor. Therefore, there is always a need for oxychlorination catalyst compositions that can run at higher optimal operating temperatures thus providing an effective way to increase the production capacity of an existing oxychlorination reactor.